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Topic Review
Technicolor
Technicolor theories are models of physics beyond the Standard Model that address electroweak gauge symmetry breaking, the mechanism through which W and Z bosons acquire masses. Early technicolor theories were modelled on quantum chromodynamics (QCD), the "color" theory of the strong nuclear force, which inspired their name. Instead of introducing elementary Higgs bosons to explain observed phenomena, technicolor models were introduced to dynamically generate masses for the W and Z bosons through new gauge interactions. Although asymptotically free at very high energies, these interactions must become strong and confining (and hence unobservable) at lower energies that have been experimentally probed. This dynamical approach is natural and avoids issues of Quantum triviality and the hierarchy problem of the Standard Model. However, since the Higgs boson discovery at the CERN LHC in 2012, the original models are largely ruled out. Nonetheless, it remains a possibility that the Higgs boson is a composite state. In order to produce quark and lepton masses, technicolor or composite Higgs models have to be "extended" by additional gauge interactions. Particularly when modelled on QCD, extended technicolor was challenged by experimental constraints on flavor-changing neutral current and precision electroweak measurements. The specific extensions of particle dynamics for technicolor or composite Higgs bosons are unknown. Much technicolor research focuses on exploring strongly interacting gauge theories other than QCD, in order to evade some of these challenges. A particularly active framework is "walking" technicolor, which exhibits nearly conformal behavior caused by an infrared fixed point with strength just above that necessary for spontaneous chiral symmetry breaking. Whether walking can occur and lead to agreement with precision electroweak measurements is being studied through non-perturbative lattice simulations. Experiments at the Large Hadron Collider have discovered the mechanism responsible for electroweak symmetry breaking, i.e., the Higgs boson, with mass approximately 125 GeV/c2; such a particle is not generically predicted by technicolor models. However, the Higgs boson may be a composite state, e.g., built of top and anti-top quarks as in the Bardeen–Hill–Lindner theory. Composite Higgs models are generally solved by the top quark infrared fixed point, and may require a new dynamics at extremely high energies such as topcolor.
  • 685
  • 28 Sep 2022
Topic Review
Technology for Science Education
The COVID-19 confinement has represented both opportunities and losses for education. Rarely before has any other period moved the human spirit into such discipline or submission—depending on one’s personal and emotional points of view. Both extremes have been widely influenced by external factors on each individual’s life path. Education in the sciences and engineering has encountered more issues than other disciplines due to specialized mathematical handwriting, experimental demonstrations, abstract complexity, and lab practices. 
  • 683
  • 22 Sep 2021
Topic Review
Statistical Ensemble (Mathematical Physics)
In physics, specifically statistical mechanics, an ensemble (also statistical ensemble) is an idealization consisting of a large number of virtual copies (sometimes infinitely many) of a system, considered all at once, each of which represents a possible state that the real system might be in. In other words, a statistical ensemble is a probability distribution for the state of the system. The concept of an ensemble was introduced by J. Willard Gibbs in 1902. A thermodynamic ensemble is a specific variety of statistical ensemble that, among other properties, is in statistical equilibrium (defined below), and is used to derive the properties of thermodynamic systems from the laws of classical or quantum mechanics.
  • 676
  • 07 Nov 2022
Topic Review
Extinction-Coefficient Modulation of MoO3 Films
This entry focused on the application of the effective medium theory to describe the extinction coefficient (Qext) in molybdenum trioxide (MoO3) doped with different kinds of plasmonic nanoparticles, such as silver (Ag), gold (Au), and copper (Cu). Usually, in studies of these materials, it is normal to analyze the transmission or absorption spectra. However, the effect of this type or size of nanoparticles on the spectra is not as remarkable as the effect that is found by analyzing the Qext of MoO3. It was shown that the β-phase of MoO3 enhanced the intensity response of the Qext when compared to the α-phase of MoO3. With a nanoparticle size of 5 nm, the Ag-doped MoO3 was the configuration that presents the best response in Qext. On the other hand, Cu nanoparticles with a radius of 20 nm embedded in MoO3 was the configuration that presented intensities in Qext similar to the cases of Au and Ag nanoparticles. Therefore, implementing the effective medium theory can serve as a guide for experimental researchers for the application of these materials as an absorbing layer in photovoltaic cells. 
  • 674
  • 20 Aug 2021
Topic Review
Firewall
A black hole firewall is a hypothetical phenomenon where an observer falling into a black hole encounters high-energy quanta at (or near) the event horizon. The "firewall" phenomenon was proposed in 2012 by physicists Ahmed Almheiri, Donald Marolf, Joseph Polchinski, and James Sully as a possible solution to an apparent inconsistency in black hole complementarity. The proposal is sometimes referred to as the AMPS firewall, an acronym for the names of the authors of the 2012 paper. The potential inconsistency pointed out by AMPS had been pointed out earlier by Samir Mathur who used the argument in favour of the fuzzball proposal. The use of a firewall to resolve this inconsistency remains controversial, with physicists divided as to the solution to the paradox.
  • 674
  • 07 Nov 2022
Topic Review
Avalanche Photodiodes and Silicon Photomultipliers of Non-Planar Designs
Conventional designs of an avalanche photodiode (APD) have been based on a planar p–n junction since the 1960s. APD developments have been driven by the necessity to provide a uniform electric field over the active junction area and to prevent edge breakdown by special measures. Most modern silicon photomultipliers (SiPM) are designed as an array of Geiger-mode APD cells based on planar p–n junctions. Modern Silicon Photomultipliers (SiPM) are designed as an array of Geiger-mode APD cells based on planar p-n junctions. However, the planar design faces an inherent trade-off between photon detection efficiency and dynamic range due to loss of an active area at the cell edges. Non-planar designs of APDs and SiPMs have also been known since the development of spherical APD (1968), Metal-Resistor-Semiconductor APD (1989), and Micro-well APD (2005). Recent development of Tip Avalanche Photodiode (2020) based on the spherical p-n junction eliminates the trade-off, outperforms the planar SiPMs in the photon detection efficiency, and opens new opportunities for SiPM improvements. Moreover, the latest developments of APDs based on electric field-line crowding and charge-focusing topology with quasi-spherical p-n junctions (2019–2023) show promising functionality in linear and Geiger operating modes.
  • 673
  • 27 Jun 2023
Topic Review
Satellite System
A satellite system is a set of gravitationally bound objects in orbit around a planetary mass object (incl. sub-brown dwarfs and rogue planets) or minor planet, or its barycenter. Generally speaking, it is a set of natural satellites (moons), although such systems may also consist of bodies such as circumplanetary disks, ring systems, moonlets, minor-planet moons and artificial satellites any of which may themselves have satellite systems of their own (see Subsatellites). Some bodies also possess quasi-satellites that have orbits gravitationally influenced by their primary, but are generally not considered to be part of a satellite system. Satellite systems can have complex interactions including magnetic, tidal, atmospheric and orbital interactions such as orbital resonances and libration. Individually major satellite objects are designated in Roman numerals. Satellite systems are referred to either by the possessive adjectives of their primary (e.g. "Jovian system"), or less commonly by the name of their primary (e.g. "Jupiter system"). Where only one satellite is known, or it is a binary with a common centre of gravity, it may be referred to using the hyphenated names of the primary and major satellite (e.g. the "Earth-Moon system"). Many Solar System objects are known to possess satellite systems, though their origin is still unclear. Notable examples include the largest satellite system, the Jovian system, with 80 known moons (including the large Galilean moons) and the Saturnian System with 83 known moons (and the most visible ring system in the Solar System). Both satellite systems are large and diverse. In fact all of the giant planets of the Solar System possess large satellite systems as well as planetary rings, and it is inferred that this is a general pattern. Several objects farther from the Sun also have satellite systems consisting of multiple moons, including the complex Plutonian system where multiple objects orbit a common center of mass, as well as many asteroids and plutinos. Apart from the Earth-Moon system and Mars' system of two tiny natural satellites, the other terrestrial planets are generally not considered satellite systems, although some have been orbited by artificial satellites originating from Earth. Little is known of satellite systems beyond the Solar System, although it is inferred that natural satellites are common. J1407b is an example of an extrasolar satellite system. It is also theorised that Rogue planets ejected from their planetary system could retain a system of satellites.
  • 672
  • 25 Oct 2022
Topic Review
Control and Upgradation of Indoor Air Quality
Due to increasing health and environmental issues, indoor air quality (IAQ) has garnered much research attention with regard to incorporating advanced clean air technologies. Various physicochemical air treatments have been used to monitor, control, and manage air contaminants, such as monitoring devices (gas sensors and internet of things-based systems), filtration (mechanical and electrical), adsorption, UV disinfection, UV photocatalysts, a non-thermal plasma approach, air conditioning systems, and green technologies (green plants and algae).
  • 672
  • 24 Feb 2023
Topic Review
Bulk and Single Crystal Growth Progress of FBS
The new iron-based superconductor (FBS) has generated enormous interest in this direction, and many research activities are currently going on with various kinds of FBS. FBS was discovered in 2008 through F doped LaFeAsO, which crystallizes with a tetragonal layered ZrCuSiAs structure, and after that, many compounds have been discovered, most of which display superconductivity through suitable doping. FBS became the second high-Tc-superconducting family after cuprate superconductors and has been the subject of extensive research into their physical nature and application potential.
  • 671
  • 14 Jan 2022
Topic Review
Proximal Sensing
Proximal sensing techniques denote several non-invasive technologies in which the target objects—in the present context, cultural heritage manufacts—are placed within a short distance of the sensor, detector or camera lens collecting the data. Depending on the technology employed and the study purpose, the sensors/detectors work in different portions of the electromagnetic spectrum, from X-ray to ultraviolet (UV), from visible (VIS) to infrared (IR) and, further, from microwave to radio.
  • 669
  • 02 Jun 2023
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